Method of coating containers



Oct. 20, 1970 GUNDERMAN ETAL 3,535,144

METHOD OF COATING CONTAINERS Filed May 22, 1968 ,Q awn INVENTORS. G/cn Gun 06rm 0r) Hora/d4. Wo/fmf Jam e5 K. Q/e/(e %AW@I M HGENT United States Patent US. Cl. 117-64 5 Claims ABSTRACT OF THE DISCLOSURE Method for applying foamed coating to liquid-filled metal containers are disclosed. Liquid-filled metal containers are coated with a foamable coating while disposed in a generally horizontal position. The foamable coating is dried, heated to foam and subsequently flattened by contact with a heated surface spaced from the container.

This invention relates to coating, and more particularly relates to an improved method and apparatus for the application of foamable coatings to generally cylindrical surfaces of liquid-filled containers.

Oftentimes it is desired to provide an insulating coating on the external surface of metal containers which contain liquid, and more particularly containers which contain foodstuffs. Such containers are particularly advantageous for use in automatic dispensing apparatus such as coin operated dispensers wherein soups and other foodstufis are dispensed hot. It is desirable that such containers have thermal insulation on the surface thereof in order that the purchaser may hold the container comfortably and to prevent cooling of the contents. The term liquid-filled as employed herein refers to a container such as a metal can which contains either a liquid such as a clear soup, or solid foodstuffs with sufficient liquid therein to provide a pourable material at serving temperature; that is, the contents of the can have a liquid which contacts the walls thereof, and at serving temperature removal of one end of the can or container permits the contents to be poured out. Generally, provision of an insulating layer on a metal container is not readily accomplished once the container has been filled and sealed. Generally, it is undesirable to provide such a coating prior to filling of the container, as many foodstuffs are autoclaved or otherwise heat treated after filling. Usually, it is desirable to provide a relatively thin coating which can be done by affixing a foamed coating to a label and subsequently applying the label to the container. However, it is frequently desirable that the foamable coating be adhered to the external cylindrical wall of the container, and beneficially, the coating may be either overlaid with a label or the foamed coating printed to provide desired indicia. Foamable coatings are those containing monocellular microspheres which expand on heating. Such expandable microspheres and coatings are described in US. Letters Patent 3,299,914 and Canadian Pat. 752,451. Substantial difficulty in foaming such coatings applied to liquid-filled metal containers is encountered when conventional techniques are employed due to uneven foaming or the requirement of substantial amounts of heat which may be sufficient to deform or even rupture the metal container.

It would be desirable if there were available an improved method for the application of a foamed coating .to the liquid-filled metal container.

It would also be desirable if there were available a continuous method of applying a foamable coating to a metal container, foaming the coating, polishing the surface thereof employing a minimal amount of heat.

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It would also be beneficial if such a method were of a generally continuous nature, simple and rapid.

These benefits and other advantages in accordance with the present invention are achieved in a method for providing a cellular synthetic resinous coating on the generally cylindrical surface of a liquid-filled metal container having a gas space therein, the steps of the method comprising providing at least one generally cylindrical metal container, applying to at least a portion of the cylindrical surface of the container a foamable synthetic resinous coating, disposing the container in a position wherein the cylindrical surface is generally horizontal, applying heat to the uppermost portion of the cylindrical surface suflicient to cause foaming of the foamable coating, subsequently passing the cylindrical surface of the container having the foamed coating thereon adjacent to a heated surface, the heated surface having a temperature sufiicient to cause collapse of the foamable coating on contact of the heated surface with the foamed coating thereby providing a foamed coating on at least a portion of the cylindrical container, the foamed coating having a generally constant thickness.

Also contemplated within the scope of the present invention is an apparatus for providing a foamed coating on the outer surface of generally cylindrical metal containers, the apparatus comprising in cooperative combination means to provide a plurality of generally cylindrical liquid-filled containers having a gas space therein, a container transport means having a first end and a second end, the transport means adapted to receive cylindrical containers from the means to provide containers, the transport means adapted to support cylindrical containers in a position wherein the axis is generally horizontal, a coating means disposed generally adjacent the first end of the transport means and adapted to provide a liquid foamable coating composition on the outer cylindrical surface of the container, means to heat an upper portion of the cylindrical surface of the container as the container rolls from the first end toward the second end of the transport means, the means providing sufiicient heat to cause the foamable coating to foam, a foam collapsing means disposed between the heating means and the second end, the collapsing means defining a surface which is in predetermined spaced relationship from the outer cylindrical surface of the can as a can rolls thereover.

Further features and advantages of the present invention will become more apparent from the following specification when taken in connection with the drawing wherein:

FIG. 1 schematically depicts an apparatus suitable for the practice of the method of the invention.

FIGS. 2-4 are schematic sectional representations of coating in various stages of processing.

In FIG. 1 there is depicted an apparatus for the practice of the method of the invention generally designated by the reference numeral 10. The apparatus 10 comprises in cooperative combination means 11 to provide a plurality of generally cylindrical liquid-filled containers, a container transport means 12 having a first end 13 and a second end 14. The transport means 12 has a generally channel-shaped configuration adapted to receive cylindrical containers such as conventional metal cans. The transport means 12 has a first edge engaging means or way 16 and a second edge engaging means or way 17 adapted to support a cylindrical container such as a container 19 and permit the container 19 to roll from the first end 13 to the second end 14 while the container 19 is in a horizontal position. A coating means 21 is disposed generally adjacent the first end 13 wherein a liquid foamable coating composition is applied to the outer cylindrical surface of a container such as the container 19. The coating means 21 comprises a coating storage vessel 22, dispensing conduit 23 and first and second dispensing nozzles 24 and 25 adapted to spray liquid coating onto the cy1indrical surfaces of the liquid-filled containers. A coating drying means or hot air source 26 is disposed between the coating means 21 and the second end 14 of the transport means 12. The drying means 26 is adapted to remove volatile liquid from the coating applied by the coating means 21. A heater means such as a radiant heater or hot air blast 28 is disposed adjacent the drying means 26 and is disposed between the drying means 26 and the second end 14. The heater 28 is spaced from conveying means 12 and adapted to permit cylindrical containers to pass beneath it. The heater 28 is adapted to provide sufficient heat to the uppermost surface of the container to cause foaming of the foamable coating as the cylindrical container progresses from the first end 13 to the second end 14 of the transport means by rolling on the terminal portions of the container. The heater 28 is in operative communication with a power supply and heat control means 29. A polishing platen or foam collapsing means 31 is disposed generally adjacent the second end 14 of the transport means 12. The collapsing means 31 has a foam contacting surface 32. The surface 32 is generally parallel to the ways or tracks 16 and 17 thereby maintaining the surface 32 at a generally constant distance from the surface of a cylindrical container rolling from the first end 13 to the second end 14 of the transport means 12. The collapsing means 31 is in operative com munication with the power source and temperature controller 29 which provides means to individually control the temperature of the radiant heater 28 and the collapsing means 31. The container 19a is shown disposed between the heater 28 and the transport means 12. A container 19b is disposed generally adjacent the collapsing means 31 and a container 19c is depicted leaving the collapsing means 31 In practice of the method of the present invention, a container such as the container 19 is disposed on the transport means 12 in such a manner that it can roll horizontally from the first end 13 toward the second end 14. A foamable coating is deposited on the cylindrical surface of the container by the coating means 21. The coating is dried by the drying means 26. The coating is then foamed as the container passes under the heater 28. The exposed surface of the foamed coating is then partially collapsed by contact with the surface 32 of the collapsing means 31 to provide a relatively smooth cylindrical foam layer on a container such as the container 196. The

quantity of foamed coating applied by the coating means 21 must be sufficiently great to foam to a sufficient thickness to contact the collapsing means 31 if an optimum smooth surface is desired. The force of gravity beneficially serves to forward the container such as the container 19 from one end to the other of the transport means 12. The rate of travel of the container is readily adjusted by varying the relative height of the ends to provide an inclined plane.

FIG. 2 is a schematic cross-sectional representation of a container 19d having a liquid foamable synthetic resinous coating 34 disposed on the surface.

FIG. 3 is a schematic representation of the container 1911 of FIG. 2 wherein the liquid coating 34 has been dried and exposed to radiant heat to provide a foamed coating 34a. The foamed coating 34a has an irregular surface 35 remote from the container 19d.

FIG. 4 is a sectional view of the container 19d after passing over the collapsing means 31 wherein the layer 34a has been partially collapsed to provide a smooth surfaced foam layer 34b.

Polymethyl methacrylate microspheres are prepared in the following manner: a polymerization reactor equipped with an agitator is charged with 100 parts of deionized water and grams of 30 percent colloidal silica dispersion. The colloidal silica dispersion is 30 percent solids and available under the trade name of Ludox HS. To this mixture is added 2.5 parts of a 10 percent solution of a copolymer prepared from diethanolarnine and adipic acid in equimolar proportions by carrying out a condensation reaction to give a product having a viscosity of about 100 centipoises at 25 C. One part of a solution containing 2.5 percent potassium dichromate is added. Methyl methacrylate is utilized as the monomer. An oil phase mixture is prepared utilizing 100 parts of methyl methacrylate and containing 20 weight percent neopentane (27.6 volume percent based on the total volume of the monomer-neopentane mixture) and 0.1 part of benzoyl peroxide as a catalyst. The oil phase mixture is added to the water phase with violent agitation supplied by a blade rotating at a speed of about 10,000 rpm. The reactor is immediately sealed and a portion sampled to determine the particle size of the resulting dispersion. The droplets appear to have diameters of from about 2 to about 10 microns. After the initial dispersion, the reaction mixture is maintained at a temperature of about C. for a period of 24 hours. At the end of this period, the temperature is lowered and the reaction mixture has the appearance of a white milky liquid similar to a chalk white milk. A portion of the mix ture is filtered to remove the resultant polymerized beads or microspheres. A portion of the beads subsequently are dried in an air oven at a temperature of about 30 C. A portion of the dried beads are heated in an air oven at a temperature of 150 C. for about 3 minutes. Upon heating, the beads show a marked increase in volume. Microscopic examination of the beads prior to foaming indicates beads having diameters of from about 2 to about 10 microns and having disposed therein a distinct spherical zone which appears to contain liquid and a small vapor space. The beads which are heated are examined microscopically and found to have diameters of from about 2 to 5 times the diameter of the original bead and to have a relatively thin, transparent wall and a gaseous center; i.e., a monocell.

A coating mixture is prepared by admixing the following components: 40.6 parts by weight of a styrene-butadiene latex, 49.3 percent solids which is a polymer of 70 weight percent styrene and 30 weight percent butadiene; 89.75 parts by weight of deionized water; 1.25 parts by weight of a 5 weight percent solution of the sodium salt of polyacrylic acid; 2.71 parts by weight of a 25 weight percent aqueous solution of isooctyl phenyl polyethylene glycol ether wherein the polyethylene glycol ether contains about 9-10 oxyethylene groups; parts by weight of wet polymethyl methacrylate expandable microspheres as a wet filter cake which is 72.8 weight percent microspheres. The resultant formulation is about 40 Weight percent solids and 80 volume percent microspheres when expanded.

A coating apparatus generally as depicted in FIG. 1 is employed wherein the coating means is a conventional paint spray gun. A plurality of sheet metal containers or cans containing soup as a liquid and a vapor space therein are rolled on an inclined plane such as the transport means 12 and the spray pattern adjusted to apply uniform coating on the surface of the cans or containers as they pass beneath the spray. The cans are protected by a suitable mask not shown in the drawing. Thirty pounds per square inch gauge of air to the paint spray gun is found adequate to provide a smooth uniform coating. Each of the cans is 2% inches in height and 8 /2 inches in circumference. The coatings applied to the can are dried by a blast of hot air and the cans passed under a heating means such as the heating means 28. Both radiant heaters and hot air blasts directed at the upper portions of the cans as they roll down the inclined plane are eminently satisfactory to cause the coatings to foam. A collapsing means 31 in the form of a steel plate heated to about 430 C. is positioned toward the second end of the transport means or inclined plane. The steel plate is positioned in such a manner that it is spaced about 15 mils from the cylindrical surface of the can and the resultant cans such as the can 190 are provided with a smooth adherent foam coating of about 15 mils in thickness. Variation of the distance of the collapsing means from the surface of the can provides variable coating thicknesses.

It is essential for optimum foaming of the coatings that the axis of generation of the cylindrical containers be disposed in a generally horizontal plane and that heat be applied to the uppermost portion. Although coatings can be formed by applying heat to other locations on the cylindrical surface of the can, the amount of heat becomes prohibitive when applied at locations other than the uppermost portion.

In a manner similar to the foregoing procedure, other foamable coatings are readily applied to liquid-filled containers having a gas space therein.

As is apparent from the foregoing specification, the present invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. For this reason, it is to be fully understood that all of the foregoing is intended to be merely illustrative and is not be construed or interpreted as being restrictive or otherwise limiting of the present invention.

What is claimed is:

1. A method for providing a cellular synthetic resinous coating on a generally cylindrical surface of a metal container having an edible liquid and a gas space therein, the steps of the method comprising providing at least one generally cylindrical metal container,

applying to at least a portion of the cylindrical surface of the container a foamable synthetic resinous coatdisposing the container in the position wherein the cylindrical surface thereof is generally horizontal,

applying heat to the uppermost portion of the cylindrical surface sufficient to cause foaming of the foamable coating, subsequently passing the cylindrical surface of the container having a foamed coating thereon adjacent to a heated surface, the heated surface, being spaced from the cylindrical surface, having a temperature suflicient to cause collapse of the exposed surface of the foamed coating on contact of the heated surface with the exposed surface of the foamed coating, thereby providing a foamed coating of generally constant thickness on at least a portion of the cylindrical container.

2. The method of claim 1 wherein the foamable synthetic resinous coating is an aqueous dispersion containing monocellular expandable microspheres.

3. The method of claim 1 wherein the coating is sprayed onto the cylindrical surface.

4. The method of claim 1 including the step of heating the uppermost portion of the cylindrical surface by radiant heat.

5. The method of claim 1 wherein the entire cylindrical surface is coated with a foamable coating.

References Cited UNITED STATES PATENTS 2,517,226 8/1950 Morrell 117132 X 2,872,349 2/1959 Hunn 1l7-132 X 3,117,693 1/1964 Vogel 117-432 X 3,286,904 11/1966 Vieth 117132 X 3,296,999 1/1967 Gamble 117132 X 3,378,507 4/1968 Sargent 117132 X 3,441,057 4/1969 Clement 1l7132 X 2,952,987 9/1960 Clauson 117132 X FOREIGN PATENTS 752,451 2/ 1967 Canada.

WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US. Cl. X.R. 

